Constant radio frequency generator



J. EVANS Jan. l1, 1938.

CONSTANT RADIO FREQUENCY GENERATOR Filed Oct. 51, 1955 2 Sheets-Sheet l Jan. 11, 1938. EVANS CONSTANT RADIO FREQUENCY GENERATOR 2 Sheets-Sheet 2 Filed Oct. 51, 1935 arll l lllllllllvV/ll/IVO V M M COOL/1V6 FL U/D Patented Jan. 11, 1938 UNETED STATES John. Evans, @ollingswcod, N. J., assigncr to Itadre Corporation of America, a corporation of Delaware Application October 31, 1935, serial No. 47,563

20 Claims.

My invention relates broadly to radio transmitters. More particularly my invention deals with a generator of constant radio frequency.

An increasing number of radio transm ters 5 has brought the requirement that each trans" mitter maintain, within very close limits, its assigned frequency. Deviation from assigned frequencies causes interference and lessens the efficiency of communication. Transmitters operating on frequencies of the present day broadcast range employ piezo-eleotric crystals for stabilizing their frequency. Such piece-electric control is not entirely satisfactory at frequencies of the order of 25 megacycles and upward.

I am aware of the use of resonant lines for controlling the frequency of oscillators. Resonant lines of the order of one quarter wave length have been used with and without temperature control for stabilizing the frequency of vacuum tube oscillators. The arrangement generally em ployed is to connect a resonant line to the input of a thermionic tube. The output of the tube is loaded with an inductive reactance. In a circuit of this type the effective input impedance depends upon the amplification .factor of the tube,

the output load, and other factors which may vary and affect the constancy of the oscillatory frequency. My invention embodies means for minimizing these efiects.

One of the objects of my invention is to generate constant frequency oscillations.

Another object of my invention is to embody in circuit means for generating oscillations whose frequency will be constant throughout a wide range of operating temperatures.

A further object is to improve the efficiency of a constant high frequency transmitter.

A still further object is in the embodiment of my invention in circuits which employ novel L) temperature compensating means.

Additional objects will be apparent from the accompanying specification, drawings and claims.

My invention may be best understood by reference to the accompanying drawings, in which Figure I is a schematic diagram of a trans mitter circuit embodying my invention,

F II is a view, partly in section, of a transmi embodying my invention,

III is a schematic diagram of the cathode .1; heater circuit used in Fig. II, and

IV a more detailed illustration. of the thermionic tube shown in Fig. II.

In Fig. I, a thermionic tube 5 having cathode 3. grid 5, and anode l electrodes is connected as 5.; follows: The cathode is heated by any suitable (Cl. Zoe-36) source which is shown as a battery 9 but may be a source of alternating current. The cathode is by-passed by a capacitor ii. The grid electrode connected to a suitable point on the inner electrode it of a concentric quarter wave line it. This quarter wavelength is measured from the open end. of electrode is to the cross piece it. The inner electrode is connected to the outer electrode i 'i of the concentric line by a conductive member iii. The cathode 3 is connected to the outer member by a grid leak resistor 2i which preferably bypassed by a capacity 23.

The anode circuit consists of a battery 25, or other suitable source of power, whose negative terminal is connected to the cathode. The positive terminal of the power source is connected through a radio frequency choke coil 21 to the anode electrode l. The anode battery may be bypassed by a capacitor 29. An extension 3! of the outer member of the concentric line houses the anode load circuit. The extension end of the outer member of the concentric line is closed by a conductor 33. In this extension a pair of conductor elements til-32 are fixed to the centers of the conducting members Ill-33, which close the line. A pair of condenser armatures 38-41 are fixed to the free ends of the pair conductor elements. The outer member ll and the pair of inner conductor elements 35-31 form, in effect, a toroidal inductor. This toroidal inductor and condenser form the anode load circuit. The tuned anode load circuit is connected to the anode by a capacitor 53 between the anode electrode I and one of the armatures 39. The outer member is connected to the anode battery by a capacitor 45.

While the theory of operation is substantially that of a triode oscillator in which the frequency is primarily determined by the constants of the circuits, I shall describe certain differences which contribute to the results I have obtained. In an ordinary tuned grid -tuned plate oscillator, the coupling between the grid circuit and the plate circuit is the capacity between grid and plate. The feedback effects, through the grid to plate capacity, required to sustain oscillations, are only obtained in the proper phase when the plate circuit load. inductive. In this arrangement, the effective input capacity is dependent upon. the amplification factor of the tube and the plate cir cuit load. Any change in either of these elements affects the frequency of oscillation. Oscillators of this type have notoriously poor frequency regulation for the reasons set forth.

Feedback in the circuit of Fig. I is not entirely lib dependent on the grid-anode capacity. The conductive member 29 is common to the grid and anode circuits. This common conductive connection acts as a feedback coupling. With this common coupling, the grid circuit may be tuned to a. quarter wave length by a suitably propon tioned line 55. The anode circuit is made resonant to the fundamental frequency although connected to a circuit equivalent to a half wave length, and will feed back energy in the proper phase to sustain oscillations. The grid and anode circuits are therefore in the proper phasal relation to insure maximum coupling. Since the system will not generate oscillations when the tuned anode load circuit offers a capacitive reactance, I prefer to adjust the anode load circuit slightly on the inductive side of resonance.

I prefer to avoid the use of mica insulation in capacitors carrying the oscillatory energy as mica has a deleterious effect on frequency stability and power factor. In the oscillatory circuits of Fig. I extremely high efficiency is obtained by the use of substantial copper conductors and the avoidance of dielectric losses. The grid lead is connected to the optimum feedback position in the grid circuit. I have further increased the efficiency of the oscillator by an effective arrangement of short leads. The preferred embodiment of my invention will be described more in detail in connection with Fig. II.

In Fig. II, a metallic end plate 5! is suitably insulated from a grounded metallic base 53. The end plate and the base form the armatures of a bypass capacitor 55. An outer electrode 51 of a concentric line is fastened to the end plate by bolting, brazing, or the like. The opposite end of the outer electrode is closed by a metal head member 59. This head member may be secured to the outer electrode 5! by bolting or any means insuring a good mechanical and low resistance electrical connection. Intermediate the ends of the outer electrode is fastened a conductor 6| which divides the outer electrode into two sections 68, Each of these sections preferably includes an expansion joint El, 69. These expansion joints may be formed by spinning one or more concentric corrugations in each section of the outer electrode. All of the parts thus far described are preferably made of copper, although other metals may be used.

By way of example, for a transmitter operating at a frequency of the order of to megacycles, the outer electrode consists of a copper cylinder having a length of inches, an inside diameter of 12 inches, and a thickness of 4 inch. A copper cylinder of this size will expand and contract with temperature changes. Such changes will alter the electric length of the circuits and cause serious variations in frequency. The effects of temperature changes may be minimized by connecting the head and lower end plates by several rods ii of invar steel. Invar steel has a very low coefficient of expansion. The invar rods will limit the expansion of the copper to the expansion joints and thereby sub stantially maintain the electric length. At high frequencies it is desirable to compensate for variations in the length of the invar rods as will be described below.

In the lower section 63 of the concentric line, an invar steel rod '33 is fastened to the center of the dividing conductor 6|. The invar rod is surrounded by a copper conductor tube 15 which is also fastened to the dividing conductor 6|. The free terminal of tie copper tube terminates in a metallic bellows H which permits the copper tube 75 to expand with respect to the invar rod T3. The variations in configuration of the bellows, and corona discharge from the end of the inner electrode are neutralized by a corona shield 79, which surrounds the bellows. Since the outer electrode 5? and its invar rods H and the inner electrode 75 and its invar rod '13 both expand the relative spacing between the end plate of the concentric quarter wave line 15 and the corona shield will remain substantially constant thereby minimizing capacity changes.

The upper section 65 of the concentric line 5! has within it a variable capacitor 8i which may be arranged as follows: An invar rod 83 is securely fastened to the dividing conductor H. A copper armature plate 85 is fastened to the free end of the invar rod. A copper tube 8'! surrounds the invar rod 83. The copper tube is fastened to the dividing conductor and is connected to the "o armature by a metallic bellows 89. A similar invar rod 9!, copper tube 93, bellows 95, and armature 9. are arranged on the metal head member 59 but the rod and tube are threaded into the head so as to provide adjustable means for raising and lowering the upper armature with respect to the lower armature for tuning the circuit. In this section 65, as in the lower section 53, the outer electrode and its invar rods expand as the inner invar rods expand. The expansion of the outer invar rods increases the spacing of the armature plates, but expansion of the inner rods decreases the spacing. Thus the armature spacing and resulting capacitance tends to remain substantially constant.

The upper section 65 of the concentric line forms, in effect, a toroidal inductor, the armature plates 85-81 forms a capacitor 8| the combination is a timed anode load circuit. It is adjusted to be substantially equivalent electrically to a half wave length, or slightly less than twice the wave length of the grid circuit, as I prefer to keep slightly on the inductive side of resonance. The tuned anode load circuit may be coupled to an external circuit, such as a pushpull amplifier. The coupling is preferably arranged through two small capacitors 99--l0l. Each armature of the tunable anode circuit may also form an armature of the coupling capacitors. The other armatures l03l05 of each of these coupling capacitors 89I0l. are circular copper plates supported by suitable insulators 81, 109 fastened to the dividing conductor El and the head plate 59. The edges of the several armature plates are rounded to avoid the effects of corona discharge.

The circuit connections have been briefly described in connection with Fig. I. I shall here point out certain features. The thermionic tube H! is supported by brackets not shown. These brackets may be fastened to the outer electrode of the concentric line. The tube may be ofv the water cooled type. The water jacket is supplied by cooling water fed through an insulated hose H5. The anode electrode III, which is also the water jacket, is connected to the anode supply through a radio frequency choke I IS. A by-pass condenser IN is connected between the choke and the outer electrode. The exposed anode I I1 is coupled to the tuned anode load circuit by a coupling capacitor [23. This coupling capacitor is comprised of the anode itself and a copper band I25 which surrounds the anode H7, but is insulated therefrom. The copper band I25 is connected directly to the circumference of the lower armature plate by a conductor IZ'I. This connection is made through a suitable orifice I29 in the outer electrode.

The grid electrode of the thermionic tube is connected by a conductor I3I directly to an appropriate point on the inner electrode of the concentric quarter wave line. The filament or cathode of. the tube is energized by a special means I33 which will be described in connection with Fig. III. The grid leak resistor I35 is connected from the lower end plate 5I to the grounded base 53. The grid leak path may include an ammeter I31 for adjusting purposes. The grid resistor I35 is by-passed by the capacitor 55 formed by the end plate and the grounded base.

In certain cases I have found that the electric length of the grid-cathode path may be such as to include reactances which prevent the generaright.

within concentric lines.

tion of high frequency oscillations. This effect may be eliminated by virtually grounding the cathode. The method and means for virtually grounding an electrode is disclosed in copending application Serial No. 41,540, filed by John Evans on September 21, 1935 entitled Ultra high frequency oscillator and assigned to the same assignee as the present application. In Fig. III, a transformer primary 20I is connected to a source of alternating current 203. The secondary 205 of the transformer is connected to an adjustable inductor 201 which is hollow. Within the inductor is an insulated wire 209. The heating currents for the filament 2 are carried by the hollow inductor 201 and inner connecting wire 239 which are connected to the filament 2. The filament is by-passed by a capacitor 2l3. The outer inductor is connected to ground by a capacitor 2I5. The inductor is adjusted so that its effective length or inductance will resonate with the grid cathode capacitance and form a circuit of very low impedance at the lower or parasitic frequencies. At frequencies other than the resonant frequency the shunt impedance of the grid cathode circuit will be relatively low. This arrangement virtually grounds the cathode. Similar results may be obtained by tuning the inductor with a capacitor.

The thermionic tube proper is shown in Fig. IV. This tube may be an RCA Type 846, or the like. Tubes of this type are water cooled. The connections 2I1 to the water source are through electrically insulated hose connections II5 to avoid grounding the exposed anode. The grid terminal 2!!! is shown as projecting toward the The filament connections 22I extend below the tube. The lower section 223 of. the tube is class. The glass is welded to the copper anode which also acts as the water jacket. The anode coupling capacitor I23 is formed by the anode II. and the spaced copper band I25. The band supported by a suitable insulator which is not shown.

I have described a high frequency generator. The tuned circuits of this generator are arranged Temperature compensation means are included whereby the electrical length remains substantially constant. The fre quency of oscillation is very constant. In actual experiments. I have found a constancy of frequency exceeding a piezo-electric element and the required frequency multipliers. In the embodiment shown the leads are very short. Several kilowatts of power may be handled in a single generator embodying my invention.

Various modifications, such as, the substitution of different materials, copper or silver plating and the like, .and physical arrangements, within the scope of my invention will occur to those skilled in the art. I do not limit my invention to the precise devices shown and described, but intend to only limit same as required by the prior art and appended claims.

I claim as my invention:

1. An oscillation generator comprising an ainplifier having input and output terminals, 2. concentric line whose effective length is substantially equal to one-quarter of the fundamental wave connected to said input terminals, a tunable circuit connected to said output terminals including a concentric line whose electrical length is substantially half the length of the fundamental wave, means for compensating for the effects of temperature changes in said quarter wave line. and means for compensating for the effects of temperature changes in said tunable whereby there is obtained in said tunable circuit oscillations of a constant frequency corresponding to the frequency of the fundamental wave.

2. A generator of high frequency oscillations comprising a thermionic tube having input and output terminals, a concentric line whose effective length is substantially one-quarter of the fundamental wave connected to said input terminals, a tuned circuit whose electrical length is substantially hall the length of the fundamental wave connected to said output terminals and including a hollow inductor and a capacitor located within said inductor, means for compensating temperature changes in said quarter wave line, and means for compensating temperature changes in said tuned circuit, whereby there is obtained in said tunable circuit oscillations of a constant frequency corresponding to the frequency of the fundamental wave.

3. An oscillation generator comprising a thermionic tube having an input and an output circuit; a concentric line having two sections, one of said sections including a line whose length is substantially one-quarter of the fundamental wave connected to said input circuit, the other of said sections including a circuit whose electrical length. is substantially one-half of the length of the fundamental wave and connected to said output circuit; and means for compensating for the efiects of temperature changes in i the two sections of said line, whereby there is obtained in said tunable circuit oscillations of a constant frequency corresponding to the frequency of the fundamental. wave.

4. An oscillation generator comprising a thermionic tube having grid, cathode, and anode electrodes: a hollow member having two sections, one of said sections including a concentric line whose length is substantially one-quarter of the fundamental wave connected to said grid. and cathode electrodes, the other of said sections including a tunable circuit whose electrical length is substantially half the fundamental wave and coupled to said cathode and anode electrodes; and means for compensating for changes in the electrical length of said sections, whereby there is obtained in said tunable circuit oscillations of a constant frequency corresponding to the frequency of the fundamental wave.

5. In a device of the character of claim 4, means for making the grid-cathode circuit a path of low impedance for parasitic frequencies.

6. In a device of the character described a pair of circuits included within a concentric line, one of said circuits comprising a quarter wave line circuit,

having means for compensating for the efiects caused by variations in temperature, and the other of said circuits comprising a tunable circuit whose electrical length corresponds to substantially one-half the fundamental wavelength and having means for compensating for the effects caused by variations in temperature, whereby there is obtained in said tunable circuit oscillations of a constant frequency corresponding to the frequency of the fundamental wave.

'7. In a device of the character described, a pair of circuits included within a. concentric line. one of said circuits comprising a line whose effective length is substantially one-ouarter of the fundamental wave having means for compensating for the efiects caused by variations in temperature. the other of said circuits having an electrical length corresponding to substantially half the fundamental wave length. and having means for compensating for the effects caused by variations in temperature, a thermionic tube, and means coupling said thermionic tube to said circuits so that oscillations of high and constant frequency corresponding to the frequency of the fundamental wave are generated.

8. A high frequency generator comprising a- Water cooled thermionic tube havin a grid, cathode, and exposed anode. a concentric quarter wave line connected to said grid and. cathode. a tunable circuit whose electrical length is sub stantially half the fundamental wave length coupled to said anode by a capacitance formed by said anode and an armature insulated therefrom, and means for transferring high frequency energy from said tunable circuit to an external circult.

9. In a device of the character of claim 8, means for compensating for the effects of temperature changes which tend to vary the electrical lengths of said circuits.

10. A high frequency transmitter comprising a thermionic tube having grid, cathode an anode electrodes, a hollow tube closed at both ends and formed into two sections by a transverse conductor intermediate sai ends, an expansion joint in each of said sections, rods having a low coefficient of expansion linking Sold ends to limit the expansion of said tube, a rod having the same coefficient of expansion as the aforementioned rods secured within one of said sections and forming therein a quarter wave length line, a pair of rods of the same coefficient of expansion as the aforementioned rods for supporting armatures within the other of said sections and forming with said armatures a circuit electrically equivalent to a half wave length line, means coupling said quarter Wave l ngth line to said grid and cathode, and means coupling said electrically equivalent half wave len th line to said anode and cathode.

11. A device or" the character of claim 10 further characterized by a conductive coupling efiectively located between said lines.

12. In a device of the character of claim 10, means located at the end of said quarter wave line for minimizing corona discharge from said quarter wave line.

13. In a device of the character of claim 10, copper rods surrounding the tubes positioned within said line and connected expansion bellows to free ends of said rods.

14. In a device of the character of claim 10, means for virtually grounding said cathode electrode.

15. A concentric line resonator comprising an outer hollow conductor and an inner hollow c0nductor, means for mechanically connecting together said conductors at one of their adjacent ends, a rod having a low temperature coefiicient of expansion within and extending substantially the entire length of said inner conductor and mechanically connected to said means at said one end of said conductors, a metallic shield surrounding a portion of and extending beyond the other end of said inner conductor and connected to said rod, and an expansible metal bellows located within said shield and connected at one end to said shield and at its other end to said inner conductor.

16. A tuned resonator comprising a pair of inner and outer conductors coupled together more closely at one of th lr adjacent ends than at their other ends, an expansible metallic bellows attached to and extending beyond said other and an outer conductor, said outer conductor having an expansion joint in the length thereof, and two rods of low temperature coefiicient of expansion extending parallel to the length of said outer conductor, located on substantially opposite sides of said outer conductor and securely fastened to both ends of said outer conductor for maintaining the length of said outer conductor substantially constant.

19. An ultra high frequency oscillatory circuit comprising a substantially enc ed met llic surface of revolution, capacitor comprising two separated plates wihin said enclosed surface of revolution, a metallic supporting rod devoid of concentrated reaotanoe directly connect i f said plates to said surface, said rods forming an inductance which, taken to ether with said capacitor, comprise the oscillatory circuit, the adjacent ends of said rods being separated substantially by the distance between said plates, and leads capacitively coupled to said plates and extending externally of said surface tion.

20. An ultra high frequenc oscillatory circuit comprising a substantially e losed metallic surface of revolution, a capacitor omprlsing two separated plates within sai' enclosed surface of revolution, a hollow metallic supporting rod devoid of concentrated reactance co necting each of said plates to said surface, expansible metal bellows between each plate and its supporting rod, and a rod of low temperature coeflicient of expansion located within each sup tingrod and mechanically linked to its associated and said surface of revolution, ....d supporting rods forming an inductance which, taken together with said capacitor, comprise the oscillatory circuit.

of revolu- JOHN EVANS.

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